Sputtering system and method including an arc detection

ABSTRACT

A sputtering system that includes a sputtering chamber having a target material serving as a cathode, and an anode and a work piece. A direct current (DC) power supply supplies electrical power to the anode and the cathode sufficient to generate a plasma within the sputtering chamber. A detection module detects the occurrence of an arc in the sputtering chamber by monitoring an electrical characteristic of the plasma. In one embodiment the electrical characteristic monitored is the impedance of the plasma. In another embodiment the electrical characteristic is the conductance of the plasma.

FIELD

The present disclosure relates generally to plasma-based sputteringsystems, and more particularly to a sputtering system that employs anarc detection system for detecting when an arc is occurring within a DCplasma sputtering chamber.

BACKGROUND

With the increasing demand for optical and disk media such as CD, DVD,MD, MO, DLC films and hard disks, the importance of the sputteringprocesses that are used in the manufacture of these media continues toincrease. There are numerous types of sputtering systems, all of whichare employed to deposit insulating or conductive coatings on devicesranging from semiconductors to drill bits. The films that are generallyapplied to optical and disk media are typically created with asputtering process having limited control over the sputtering gas. Morespecifically, with present day sputtering systems and methods, asignificant fraction of atmosphere and petrochemical volatilities arepresent in the sputtering chamber at the beginning of the sputteringprocess.

In a typical DC plasma-based sputtering system, atmosphere is introducedinto a plasma chamber at the very beginning of the sputtering process.The atmosphere combines with freed target material present within thechamber. The resulting compound, typically comprising oxides andnitrides, may form a film on the surface of the target. This is referredto as “target poisoning”, and will cause arcing between the cathode andanode within the sputtering chamber. Arcing, although inevitable in a DCplasma-based sputtering system, is a mixed blessing. The arc oftenremoves the poisoning from the target but it may also generateundesirable particles that can damage the work piece upon which materialis being deposited. Additional sources of arcing include contaminantswithin the sputtering chamber such as moisture, atmospheric gases andinclusions. Outgassing may also cause arcing. Outgassing is a conditionthat arises when gasses and/or impurities trapped in the work piecebeing coated, or in the target material itself, is released during thesputtering process.

In the past, numerous detection methods have existed for determiningwhen an arc is occurring in the plasma chamber. These methods haveinvolved using voltage limits and/or current limits to detect when thevoltage or current reaches a predetermined threshold. Other methods forarc detection have involved sensing the change in the output voltageover time (dV/dT), and/or sensing the change in output current over time(dI/dT) of the DC supply. Each of the above mentioned methods has beenimplemented with several distinct techniques and varied circuitry. Eachmethod, however, has limitations that can interfere with accurate arcdetection and result in either false arc detection or failure to detectan arc occurrence. For example, when using a voltage limit baseddetection system, depending on the process and the strike conditionencountered, it may not be possible to turn on the voltage limitdetection circuit fast enough to detect the strike condition. Also, ifthe sputtering process uses a low DC output voltage setting in relationto the voltage threshold selected, then the reduced DC output voltagemight reach a point where it starts to interfere with reliable operationof the arc detection circuit. More specifically, the DC supply voltagemight be low enough so that the arc detection erroneously senses that anarc condition is occurring. Also, when an ignition finally occurs in theplasma, or the plasma has come out of an arc, care in enabling thevoltage limit check circuitry has to be taken otherwise a false arc maybe indicated.

When using a dV/dT or dI/dT based arc detection monitoring, one islooking for a fast transient voltage or current output from the DCsupply, and relying on the detection of the fast delta in either outputvoltage or output current from the DC supply to signal that an arccondition has occurred. However, with a dI/dT based system, instancesmay be encountered where as the arc that has occurred is relatively slowmoving, and therefore doesn't produce a fast delta in the sensed outputcurrent from the DC supply. In the industry, these types of arcs havebeen referred to as “fireball arcs” or “high impedance” arcs. Withoutthe fast delta in output current, the dI/dT detection system may fail todetect the occurrence of an arc. A dV/dT based detection circuitsimilarly suffers from the limitation of being sometimes unable todiscern the occurrence of a slow moving arc because of the slow drop inthe sensed output voltage of the DC supply.

SUMMARY

In one aspect the present disclosure relates to a sputtering system. Thesystem may include: a sputtering chamber having a target materialserving as a cathode, and the sputtering chamber further including ananode and a work piece; a direct current (DC) power supply for supplyinga electrical power to the anode and the cathode sufficient to generate aplasma within the sputtering chamber; and a detection module thatdetects the occurrence of an arc in the sputtering chamber by monitoringan electrical characteristic of the plasma.

In another aspect the present disclosure relates to a sputtering systemthat comprises: a sputtering chamber having a target material serving asa cathode, and the sputtering chamber further including an anode and awork piece; a direct current (DC) power supply for supplying electricalpower to the anode and the cathode sufficient to generate a plasmawithin the sputtering chamber; a voltage sensor circuit adapted to sensean output voltage of the DC power supply being applied to across thecathode and the anode; a current sensor circuit adapted to sense anoutput current from the DC power supply that is flowing between thecathode and the anode during a sputtering operation; and a detectionmodule responsive to the sensed current signal, to the sensed voltagesignal, and further responsive to a pre-selected resistance, for usingthe sensed voltage signal, the sensed current signal and thepre-selected resistance to determine when the impedance has dropped to alevel within the sputtering chamber that indicates an arc condition isoccurring.

In still another aspect the present disclosure relates to a method forforming a sputtering system. The method may comprise: providing asputtering chamber having a target material serving as a cathode, andthe sputtering chamber further including an anode and a work piece;supplying direct current (DC) power to the anode and the cathodesufficient to generate a plasma within the sputtering chamber; anddetecting the occurrence of an arc in the sputtering chamber bymonitoring an electrical characteristic of the plasma during asputtering operation being performed within the sputtering chamber.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a block diagram of a sputtering system constructed inaccordance with one embodiment of the present disclosure;

FIG. 2 is a signal diagram showing the voltage and impedance waveformsassociated with the output of a DC power supply feeding a plasmachamber, when an arc occurs;

FIG. 3 is a schematic diagram of one embodiment of a detection module ofthe present disclosure designed to monitor the impedance of the plasmawithin the sputtering chamber during a sputtering operation; and

FIG. 4 is a schematic diagram of another embodiment of a detectionmodule that monitors the conductance of the plasma within the sputteringchamber during a sputtering operation.

DETAILED DESCRIPTION

The following description of various embodiments is merely exemplary innature and is in no way intended to limit the present teachings,application, or uses.

Referring to FIG. 1, a DC sputtering system 10 in accordance with oneembodiment of the present disclosure is shown. The system 10 is used todeposit a coating on a work piece 12. The work piece 12 may comprise anoptical disk storage media such as a compact disc (CD), a digital videodisc (DVD), a drill bit, a glass panel, a cutting tool, a toy, or anyother component or substrate that requires a sputtered surface film forits use and operation. Sputtering system 10 includes a sputteringchamber 14 that provides a controlled environment for the depositionprocess. A vacuum pump 16 is coupled to a port 14 a in the sputteringchamber 14 and used to maintain a controlled internal pressure withinthe sputtering chamber. Sputtering target 18, configured as a cathode(and hereinafter referred to simply as the “cathode” 18), serves as asource of material for the sputtered coating that will be applied to thework piece 12 during the sputtering process.

Another piece of conductive material disposed within the sputteringchamber 14 is the anode 20. Cathode 18 and anode 20 are coupled to theoutput of a DC power supply 22 that supplies a high DC voltage(typically between about 200 Vdc-1000 Vdc, but is not limited to thisrange) across the cathode 18 and anode 20. The DC voltage output fromthe DC power supply 22 is supplied across the cathode 18 and anode 20via output signal lines 24 and 26, respectively. This induces a plasmastate within the sputtering chamber 14. The cathode 18 may be comprisedof aluminum (Al) or any other material suitable to be employed in asputtering process. Other suitable materials may be comprised of, forexample, Gold (Au), Tantalum (Ta), and Titanium (Ti), just to name afew.

In a typical sputtering process the atmospheric gas introduced at thestart of the process is a contaminant. The contaminant may be introducedwhen a part is loaded into the chamber 14. A controlled amount of asputtering gas for providing anions that flow within the plasma is alsosupplied to the sputtering chamber 14. Typically argon or another noblegas is used as the sputtering gas, although the present disclosure isnot limited to use with any specific type of sputtering gas.

FIG. 1 also illustrates one exemplary manufacturing application wherethe work piece 12 forms a circular optical disk that needs to be coatedwith a sputtered film. For this specific application an outer shield 28and an inner shield 30 are positioned in the sputtering chamber 14adjacent to the work piece 12 and serve to mask an outer edge 12 a andan inner edge 12 b, respectively, of the work piece 12. The shields 28and 30 provide well defined outer and inner radii for the work piece 12.The outer shield 28 is preferably positioned between the cathode 18 andthe work piece 12 to prevent the deposition of sputtered material on theouter edge 12 a. The inner shield 30 is positioned within the outershield 28 and closely adjacent to an inner radius 12 b of the work piece12 to prevent coating the inner edge with sputtered material from thecathode 18.

DC power supply 22 provides the electrical energy necessary for thesputtering process to occur. The DC power supply 22 converts unregulatedAC line power to regulated DC power suitable for initiating thesputtering process within the sputtering chamber 14. The DC power supply22 may comprise any suitable form of power supply, for example, aswitched mode power supply, an SCR power supply or a diode-transformerpower supply. However, the scope of the present disclosure is notlimited by the specific type of DC power supply employed. As will berecognized by those skilled in the art, the nominal voltage generated bythe DC power supply 22 needs to be suitable for the specific targetmaterial and sputtering operation being performed. Therefore, the scopeof the present disclosure contemplates sputtering processes that employa wide range of DC supply voltages.

In the system 10, the actual deposition of the sputtered coating fromthe cathode 18 onto the work piece 12 requires the ignition of a plasmawithin the chamber 12. The plasma is created by applying a voltagebetween the anode 20 and the cathode 18 that is sufficiently high tocause ionization of at least a portion of the sputtering gas containedwithin the chamber 14. The intense electric field associated with theapplied DC voltage strips electrons from the gas atoms, creating anionsand electrons that flow within the plasma. The anions are accelerated bythe steady-state electric field created within the sputtering chamber 14into the cathode 18 with sufficient kinetic energy to cause the anionsto displace atoms from cathode 18. Some of the freed atoms from thecathode 18 combine with atmosphere that is present within sputteringchamber 14 at the beginning of the sputtering process. The remainingfreed atoms from the cathode 18 that are uncombined also dispersethroughout the sputtering chamber 14 and coat the exposed surfaces ofthe work piece 12. Throughout the above-described sputtering processarcing occurs intermittently due to various factors such as targetpoisoning, outgassing from work piece 12, contaminants, and the presenceof material flakes within the sputtering chamber 14.

In sputtering applications an “arc” refers to a plasma state sustainedby a relatively low voltage and high current. When an arc occurs withinthe sputtering chamber 12 the impedance of the plasma existing betweenthe cathode 18 and the anode 20 dramatically decreases. This effectivelycauses a zero or near zero “impedance” condition to occur which causes arapid rise in the cathode 18 current. More specifically, in the arcregion, the plasma impedance collapses due to the regenerative gain andthe thermal ionization of the arc discharge. All available energy beingsupplied by the DC power supply 22 is then driven into the arcdischarge, which in turn generates extreme temperatures and even morethermal ionization. This in turn continues to lower the arc impedance ofthe chamber. It is the collapse of plasma energy (sheath) to essentiallya point arc discharge that generates the massive energy densities whichlead to particulates and damage of the target or work piece 12.

The relationship between the DC power supply output voltage and theimpedance (i.e., resistance) of the plasma during an arc condition isalso shown in the graph of FIG. 2. In FIG. 2 the DC power supply outputvoltage is depicted by a voltage waveform A having portions A₁ and A₂.Waveform portion A₁ represents the DC power supply 22 output voltageprior to the occurrence of an arc within the sputtering chamber 12, andportion A₂ illustrates the DC supply voltage subsequent to the arcevent. The impedance of the plasma “seen” by the DC power supply 22(i.e., effectively the cathode 18 to anode 20 impedance) is representedby waveform B having portions B₁ and B₂. The horizontal axis, X, of FIG.2 represents time and the vertical axes, Y and Y′, represent impedanceand voltage, respectively.

As discussed previously, when an arc occurs, the impedance from cathode18 to anode 20, as illustrated in FIG. 1, dramatically decreases. Asshown in FIG. 2, the cathode 18 to anode 20 impedance is reduced sharplybetween waveform portions B₁ and B₂ indicating the occurrence of an arcwithin the plasma. During the same interval of time, the DC power supply22 voltage output level experiences a sharp increase from waveformportion A₁ to portion A₂.

To detect the occurrence of an arc during the sputtering process thesystem 10 includes a detection module 32 that simultaneously monitorsboth the output voltage and the output current from the DC power supply22. A sensed voltage signal is provided by a voltage sensor circuit 34positioned across the output signal lines 24 and 26. A current sensorcircuit 36 is disposed in series with output signal line 26 and providesa sensed current signal. As will be described in greater detail in thefollowing paragraphs, the detection module 32 uses the sensed voltage,sensed current, and a pre-selected resistance value to detect when theimpedance of the plasma has fallen to a level indicating that an arc hasoccurred. In this manner the detection module 32 can effectively monitorthe state (i.e., the impedance) of the plasma within the chamber 14during the sputtering process, and more specifically the impedancebetween the cathode 18 and anode 20. This is in contrast to conventionalarc detection systems and methods that have relied on a voltage limit, acurrent limit, or monitoring the rate of change of the voltage (dV/dT)or current (dI/dT) to detect the occurrence of an arc.

With reference to FIG. 3, one embodiment of the detection module 32 isshown in detail. The detection module 32 includes a pre-selectedresistance value, “R”, a digital multiplier 38 and a comparator 40. Thedigital multiplier 38 receives an input from the current sensor circuit36 that is indicative of the real time output current (I) being suppliedfrom the DC power supply 22, as well as the pre-selected resistancevalue R. The value of R is selected based on previously observedcharacteristics of the DC output voltage and output current for aspecific DC Plasma application when an arc is known to be occurringwithin the chamber 14, or after study of the normal operation of thePlasma. The resistance value R acts as a scaling factor, or multiplier,that tunes the detection module 32 to the output of the particular DCpower supply being used and the known arcing characteristics of aspecific sputtering application. Although the specific value of R isdependent on a specific application, it is anticipated that in manyinstances an appropriate value will be in the range of about 1 ohms-6ohms, but not limited to this range. The digital multiplier 38multiplies these values to form an I×R “trip” voltage. This trip voltageis applied to the non-inverting (+) input of the comparator 40. Theinverting input (−) of the comparator 40 receives the sensed voltagesignal from the voltage sensor circuit 34 that is indicative of the realtime DC voltage output signal (V) being applied across the cathode 18and the anode 20.

When an arc occurs, the trip voltage being the input to thenon-inverting (+) input of comparator 40 rises significantly over a veryshort period of time. The comparator 40 continuously compares the I×Rtrip voltage being applied to its non-inverting input against thesampled voltage signal from the voltage sensor 34 that is being appliedto its inverting input. Comparator 40 provides an output 42 that forms a“trip indicator” signal. The trip indicator signal signifies that theI×R trip voltage has risen to a point where it is equal to or greaterthan the sampled DC voltage signal on the inverting input of thecomparator 42. This condition signifies that the impedance of the plasmabetween the cathode 18 and anode 20 has dropped sufficiently to a pointwhere it defines accurately, consistently, and repeatably that an arc isin a state of occurence.

When the detection module 32 generates the trip indicator signal, thissignal could optionally be applied to a controller that is able toeither shut down the DC power supply 22 or temporarily reduce the DCoutput voltage of the supply. The trip indicator signal couldalternatively be applied to a different component of the sputteringsystem 10 in an effort to temporarily interrupt or reduce the DC outputpower to ameliorate the arc condition.

For the embodiment illustrated in FIG. 3, it is important to note thatdetection module 32 is preferably disabled for a short time period,typically between about 10 μs-100 μs, at the initial startup of the DCpower supply 22. This is done to avoid the occurrence of a false arcindication. If the detection module 32 was to be energizedsimultaneously with the DC power supply 22 a condition would likelydevelop at the instant of turn-on where the comparator 40 is receiving azero voltage signal on its inverting input and a zero voltage signal onits non-inverting input, which could thus immediately cause thecomparator to generate a false trip indicator signal at its output 42.This very brief delay at startup may be achieved through a suitablehardware control system or a software control that delays, for a briefinstant, the turn-on of the comparator 40 for a time that will allow theDC output voltage of the DC power supply to ramp up to a predesignatedvalue. Once the detection module 32 is operational, it will not generatea trip indicator signal unless an arc condition is detected.

Therefore, the detection module 32 is able to monitor, in real time, thefluctuating impedance of the plasma within sputtering chamber 14 duringthe operation of sputtering system 10. By determining the trip voltageas a function of R, which is fixed, and the measured current at theoutput of DC power supply 22, the arc detection or trip indication levelof detection module 32 becomes directly proportional to the fluctuatingimpedance of the plasma generated within the sputtering chamber 14 asthe sputtering process in carried out.

A particular advantage of the detection module 32 is that by using apre-selected resistance value, the voltage trip level may be easilytailored to various sputtering systems employing different DC supplyvoltages. The detection module 32 does not suffer from the limitationsthat can affect operation of voltage limit systems, current limitsystems, dI/dT based systems or dV/dT based systems. Since the voltagetrip indicator makes use of sampled DC output voltage and output currentsignals that are representative of the output of the DC power supply 22,the voltage trip level is able to change or “float” in relation to theoutput from the DC power supply 22. Thus, if power from the DC powersupply 22 needs to be reduced for a particular sputtering operation, thetrip voltage will be automatically scaled down because of the drop inoutput current that the digital multiplier 38 will see from the currentsensing circuit 36. Furthermore, the detection module 32 is notdependent on the occurrence of a sharp drop (with respect to time) ofeither the DC output voltage or the output current from the DC powersupply 22. Thus, the detection module 32 is able to detect theoccurrence of “fireball” or “high impedance” arcs that generally occurwithout a sharp change in the sensed voltage or current. The detectionmodule 32 also is not susceptible to providing trip signals thaterroneously indicate the occurrence of an arc.

Still another advantage of the detection module 32 is that since itmonitors the impedance of the plasma, it is essentially immune tospurious operation that previously developed detection system havesuffered from as a result of focusing on only a sensed voltage, or ononly a sensed current. Neither the end of a strike condition nor thetime during a recovery from an arc will create a condition in the plasmawhere its impedance will drop sufficiently to approach the value of R.As a consequence of this limitation, the detection module 32 is keptfrom functioning improperly during “end of strike” and “recovery”conditions while the sputtering process is being carried out.

In the embodiments described above it will be appreciated that while thedetection module 32 may utilize R at a specific power level forsputtering system 10 to identify the existence of an arc, the scope ofthe present disclosure is not limited to only monitoring impedance ofthe plasma. For example, the detection module 32 could just as readilybe configured to monitor the conductance (i.e., 1/resistance or “G”) ofthe plasma. Such an embodiment of the detection module is shown in FIG.4 where the detection module is labeled 32′. Other components of thedetection module 32′ in common with those of FIG. 3 are labeled withcorresponding reference numbers that are also designated with a prime(′) symbol. In this implementation when an arc occurs the conductance ofthe plasma increases significantly, and essentially inversely to theimpedance of the plasma. The trip signal comprises a trip current thatis generated by multiplying the sensed voltage signal (V) by 1/R, where1/R represents a pre-selected conductance value. The trip current isapplied to the inverting input (−) of the comparator 40′ while thesensed current signal is applied directly to the non-inverting (+) inputof the comparator 40′. When the sputtering process is taking place andno arcing is occurring, the trip current will normally be higher thanthe sensed current signal. However, when an arc occurs the conductanceof the plasma will rise significantly, and typically over a short periodof time. The comparator 40′ senses this condition when the sensedcurrent signal on its non-inverting input equals or exceeds the tripcurrent applied to its inverting input. The comparator 40′ thengenerates a trip indicator signal 42′ indicating that arcing isoccurring.

The various embodiments of the detection module 32 may be implemented ina single integrated circuit or by discrete components. Additionally,detection module 32 may be implemented in connection with software,firmware or other hardware depending on the needs of a specificapplication.

The foregoing description is merely exemplary in nature and, thus,variations that do not depart from the gist of the teaching are intendedto be within the scope therein. Such variations are not to be regardedas a departure from the spirit and scope of the teachings presentedherein.

What is claimed is:
 1. A plasma system comprising: a direct current (DC)power supply for supplying electrical power to an anode and a cathode ofa plasma chamber wherein the cathode serves as a target material, theelectrical power being sufficient to generate a plasma within saidplasma chamber; and a detection module configured to detect anoccurrence of an arc in the plasma chamber by monitoring at least one ofimpedance and conductance of said plasma, the detection module isfurther configured to receive a sensed voltage signal from a voltagesensor circuit or a sensed current signal from a current sensor circuit,one of the voltage sensor circuit or current sensor circuit connected tocommunicate the respective sensed voltage signal or sensed currentsignal to a multiplier, the multiplier configured to communicate a tripsignal to a comparator; wherein the detection module is furtherconfigured to compare by the comparator one of the sensed voltage signalor the sensed current signal to said trip signal, such that when thesensed voltage signal is compared by the comparator to said trip signal,said trip signal varying in accordance with the sensed current signal,said trip signal is obtained by the multiplier multiplying said sensedcurrent signal by a pre-selected resistance value, wherein a tripindicator signal is generated indicating arcing is occurring if thesensed voltage signal crosses a threshold determined in accordance withthe trip signal; or when said sensed current signal is compared by thecomparator to said trip signal, said trip signal varying in accordancewith the sensed voltage signal, said trip signal is obtained by themultiplier multiplying said sensed voltage signal by a pre-selectedconductance value wherein the trip indicator signal is generatedindicating arcing is occurring if the sensed current signal crosses athreshold determined in accordance the trip signal.
 2. The system ofclaim 1, wherein the voltage sensor circuit is configured to sense avoltage applied across said anode and said cathode, and to provide thesensed voltage signal to said detection module; and the current sensorcircuit is configured to sense a current flowing between said cathodeand said anode within said plasma chamber, and to supply the sensedcurrent signal to said detection module.
 3. The system of claim 2,wherein the multiplier includes a first input for receiving one of saidsensed voltage signal or said sensed current signal, and a second inputfor receiving one of the pre-selected resistance value or saidpre-selected conductance value and performing the multiplying togenerate the trip signal.
 4. The system of claim 3, wherein saidmultiplier comprises a digital multiplier.
 5. The system of claim 1,further including a vacuum pump coupled to a port in said plasma chamberfor maintaining a desired pressure within said plasma chamber.
 6. Thesystem of claim 1, wherein said plasma chamber further includes: a firstshield for covering a first portion of a work piece in the plasmachamber; and a second shield for covering a second portion of said workpiece.
 7. The system of claim 6, wherein said work piece comprises acircular disc shaped work piece with a central opening, and said firstshield is shaped to cover an outer radius of said work piece, and saidsecond shield is configured to cover an inner radius of said work piece.8. A plasma system comprising: a direct current (DC) power supplyconfigured to supply electrical power to an anode and a cathode of aplasma chamber wherein the cathode serves as a target material, theelectrical power being sufficient to generate a plasma within saidplasma chamber; a voltage sensor circuit communicating with the DC powersupply and configured to sense an output voltage of said DC power supplybeing applied to across said cathode and said anode; a current sensorcircuit communicating with the DC power supply and configured to sensean output current from said DC power supply flowing between said cathodeand said anode during a plasma operation; and a detection modulecommunicating with the voltage sensor circuit and the current sensorcircuit and configured to receive a sensed current signal that varies inaccordance with the sensed output current, a sensed voltage signal thatvaries in accordance with the sensed output voltage, the detectionmodule configured to respond to said sensed voltage signal, said sensedcurrent signal and one of a pre-selected resistance or a pre-selectedconductance and further configured to determine when an impedance in theplasma chamber has dropped to a level within said plasma chamber thatindicates an arc condition is occurring, the detection module including:a multiplier having a first input configured for receiving one of saidsensed voltage signal from said voltage sensor circuit or said sensedcurrent signal from said current sensor circuit, and a second inputconfigured for receiving one of said pre-selected resistance or saidpre-selected conductance, and configured to multiply one of; said sensedvoltage signal by said pre-selected conductance to generate a tripsignal varying in accordance with the sensed voltage signal; or saidsensed current signal by said pre-selected resistance to generate thetrip signal varying in accordance with the sensed current signal; and acomparator communicating with the multiplier, the comparator having oneof: a first input configured for receiving said sensed voltage signalfrom said voltage sensor circuit and a second input configured forreceiving the trip signal; or the first input configured for receivingsaid sensed current signal from said current sensor circuit and a secondinput configured for receiving the trip signal, and comparing said tripsignal to said sensed voltage signal or trip signal to said sensedcurrent signal, the comparator configured for generating a tripindicator signal indicating an arc condition is occurring when said tripsignal crosses a threshold determined in accordance with said sensedvoltage signal or when said trip signal crosses a threshold determinedin accordance with said sensed current signal.
 9. The system of claim 8,wherein: the trip signal changes in accordance with a magnitude of saidsensed current signal and the comparator generates the trip indicatorsignal when said trip signal reaches a level that is one of equal tosaid sensed voltage signal and greater than said sensed voltage signal.10. The system of claim 8, further comprising a vacuum port incommunication with said plasma chamber for controlling an internalpressure of said plasma chamber.
 11. The system of claim 8, wherein saidplasma chamber comprises a first shield for covering a first portion ofa work piece in the plasma chamber and a second portion for covering asecond portion of said work piece during a fabrication process.
 12. Thesystem of claim 11, wherein said work piece comprises a circular discshaped work piece with a central opening, and a first shield is shapedto cover an outer radius of said work piece, and a second shield isconfigured to cover an inner radius of said work piece.